The present invention relates to downhole drilling, and more particularly, to systems and methods for transmitting power to components of a downhole drill string.
Downhole sensors, tools, telemetry components and other electronic components continue to increase in both number and complexity in downhole drilling systems. Because these components require power to operate, the need for a reliable energy source to power these downhole components is becoming increasingly important. Constraints imposed by downhole tools and the harsh downhole environment significantly limit options for generating and providing power to downhole components.
Batteries provide one potential energy source to power downhole components. Batteries, however, may be hindered by their inherently finite life and the need for frequent replacement and/or recharging. This may be especially problematic in downhole drilling applications where access to batteries requires tripping and disassembly of the drill string. Battery function may also be impaired by extreme temperatures, pressures, or other conditions found downhole. Many types of batteries may be unable to reliably operate in downhole conditions. Furthermore, batteries may be required everywhere electronic equipment is located downhole, requiring large numbers of batteries and significant time for installation and replacement.
Another approach is to transmit power along the drill string using cables or other transmission media. For example, power may be generated at or near the ground's surface and then transmitted to various downhole components along the drill string. This approach, however, may also have its problems and limitations. Because a drill string may extend 20,000 feet or more into the ground, power transmitted along transmission lines may attenuate to an unacceptable level before it reaches its destination.
Attenuation may occur not only in transmission lines, but in components used to transmit power across tool joints of a drill string. Because a drill string may include many hundreds of sections of drill pipe and a roughly equal number of tool joints, a power signal may attenuate significantly after traveling a relatively short distance along the drill string.
In view of the foregoing, what is needed is a system and method for reliably transmitting power to downhole sensors, tools, telemetry components and other electronic components in a downhole drilling system. Ideally, such a system and method would mitigate the problems with signal attenuation which may be present in some power transmission systems. A suitable system and method should also be able to provide reliable operation in extreme temperatures, pressures, and corrosive conditions encountered downhole. Further needed is a system and method for generating power in closer proximity to downhole components.